The present invention relates to valves, and more particularly to a modified butterfly valve having a stepped rotating vane.
Conventional butterfly valves operate by positioning a disk within a duct to control fluid flow through the duct. The disk rotates about a pivot point or axis defined by a shaft mounted within the duct. Rotation of the disk, resulting from a torque applied to the shaft, creates or reduces an opening for fluid to flow through the duct. The fluid flow can be controlled by adjusting the angle of rotation of the disk within in the duct.
In many applications making use of butterfly valves, several factors are taken into consideration when choosing a particular butterfly valve having predetermined flow characteristics for each application. One factor is the desire for an improved inherent flow characteristic, which is the ratio between the flow coefficient (Cv) and the travel in degrees of rotation of the disk. The flow coefficient Cv represents the pressure drop or flow capacity of a valve. Manufacturers of valves often publish flow coefficients together with equations for predicting flow versus pressure drop for a particular valve. The flow coefficient can be different for liquids versus gases.
A second factor that can be important in many applications is the desire for reduced noise. This is achieved by providing a higher coefficient of incipient cavitation in combination with a lower aerodynamic noise efficiency. In other words, a valve less likely to experience cavitation will have reduced noise characteristics. Cavitation occurs with a liquid flowing through a valve. Cavitation is the two-stage process of vaporization and condensation of a liquid. Vaporization of a liquid occurs when the liquid begins to boil. This is also known as flashing. In a valve, this vaporization occurs when the pressure of the liquid is lowered, instead of an increase in the temperature. As fluid passes through a valve downstream of the disk area, there is an increase in velocity or kinetic energy that is accompanied by a substantial decrease in pressure or potential energy. If the pressure in this area falls below that of the vapor pressure of the fluid flowing through the valve, vaporization occurs. Vapor bubbles then continue downstream where the velocity of the fluid begins to slow and the pressure in the fluid recovers. The vapor bubbles then collapse. Cavitation can affect flow rates and can cause mechanical damage to valves and piping. Incipient cavitation relates to the early stages of cavitation. In the early stages, the bubbles are small, and there is a hissing-type noise. Further information regarding the characteristics and consequences of cavitation can be found in Preventing Cavitation in Butterfly Valves, CHEMICAL ENGINEERING, Mar. 18, 1985, pp. 149-153.
A third factor relates to a desire for an improved dynamic torque characteristic, which reduces the amount of torque required to control the flow of fluid through the valve. As the fluid flows through the valve, a force is generated against the disk as it impedes the fluid flow. The amount of torque required to rotate the disk to open or close the valve will vary depending on characteristics of the fluid flow and the shape and orientation of the disk.
There is a need in the art for a butterfly valve having improved inherent flow characteristics, improved noise characteristics, and improved dynamic torque characteristics. The present invention is directed to further solutions that address this need.
In accordance with one example embodiment of the present invention, a valve includes a disk for controlling fluid flow inside the valve. The disk has a first vane and a second vane disposed relative to the first vane. The first vane forms a sealing surface, and the second vane forms a fluid obstructing surface. In accordance with one embodiment of the invention, the second vane is disposed along an axis extending from a pivot point of the disk. In such an embodiment, the first vane is disposed offset from the second vane. The first vane and the second vane can be substantially parallel to each other.
In accordance with another embodiment of the present invention, the disk includes an indentation along an upstream side of the disk, suitable for dynamic torque reduction. The indentation can take the form of a substantially concave curved surface, or concavity. Alternatively, the indentation can be formed from a ramp surface angled relative to a vertical axis.
In accordance with one aspect of the present invention, at least one aperture, or slot, is disposed along a downstream side of the disk for reduction of cavitation and/or aerodynamic noise.
In accordance with further aspects of the present invention, at least one of the first and second vanes can have a substantially L-shaped profile. The first and second vanes can also be formed of a cavity disposed along a periphery of the disk.
In accordance with still another aspect of the present invention, a third vane can be disposed on the disk relative to the first and second vanes. The third vane can have a second fluid obstructing surface.
In accordance with yet another aspect of the present invention, a valve is provided having a pivotable disk. A first vane is disposed on the pivotable disk and a second vane is disposed relative to the first vane on the pivotable disk. The first vane has a sealing surface and the second vane has a fluid obstructing surface. The valve can be a butterfly valve.
In accordance with the teachings of the present invention, the valve can position the second vane along an axis extending from a pivot point of the disk.
In accordance with still another aspect of the present invention, a wall of a valve housing can be substantially concave to enable the first and second vanes to rotate in close proximity to the wall. The distance between the outer periphery of the first or second vane and the wall can be gradually enlarged to provide for a desired flow characteristic.
In accordance with yet another aspect of the present invention, the first vane can provide a first pressure drop of a fluid passing through the valve and the second vane can provide a second pressure drop of the fluid passing through the valve.
In accordance with further aspects of the present invention, an indentation can be provided along an upstream side of the disk for dynamic torque reduction. The indentation can be in the form of a substantially concave curve, or a ramp angled relative to a vertical axis. At least one aperture can be disposed along a downstream side of the disk for a reduction of at least one of cavitation and aerodynamic noise. Further, at least one indentation can be disposed along a downstream side of the second vane for reduction of hydrodynamic torque.
At least one of the first and second vanes can have a substantially L-shaped profile. In addition, the first and second vanes can be formed of a cavity disposed along a periphery of the disk. A third vane can be disposed on the disk relative to the first and second vanes.